In the electronics industry, flexible substrates are quickly becoming popular as a base for electronic circuits. Flexible substrates can include a wide variety of materials, such as, for example, any of a myriad of plastics, metal foils, and glasses (e.g., Corning® glass, Willow™ glass, etc.). Once a desired electronic component, circuit, or circuits are formed over a surface of the flexible substrate, the flexible substrate can be attached to a final product or incorporated into a further structure. Typical examples of such products or structures are active matrices on flat panel displays, RFID (radio-frequency identification) tags on various commercial products in retail stores, a variety of sensors, etc.
A need exists in the art to develop a process for fabricating semiconductor devices on flexible substrates that allows for improved electrical characteristics, such as, for example, improved parametric characteristics and/or lifetime, and reduced bowing, warping, and/or distortion.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “include,” and “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, device, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, system, article, device, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
The terms “couple,” “coupled,” “couples,” “coupling,” and the like should be broadly understood and refer to connecting two or more elements or signals, electrically, mechanically and/or otherwise. Two or more electrical elements may be electrically coupled but not be mechanically or otherwise coupled; two or more mechanical elements may be mechanically coupled, but not be electrically or otherwise coupled; two or more electrical elements may be mechanically coupled, but not be electrically or otherwise coupled. Coupling may be for any length of time, e.g., permanent or semi-permanent or only for an instant.
“Electrical coupling” and the like should be broadly understood and include coupling involving any electrical signal, whether a power signal, a data signal, and/or other types or combinations of electrical signals. “Mechanical coupling” and the like should be broadly understood and include mechanical coupling of all types.
The absence of the word “removably,” “removable,” and the like near the word “coupled,” and the like does not mean that the coupling, etc. in question is or is not removable.
The term “bowing” as used herein means the curvature of a substrate about a median plane, which is parallel to the top and bottom sides, or major surfaces of the substrate. The term “warping” as used herein means the linear displacement of the surface of a substrate with respect to a z-axis, which is perpendicular to the top and bottom sides, or major surfaces of the substrate. The term “distortion” as used herein means the displacement of a substrate in-plane (i.e., the x-y plane, which is parallel to the top and bottom sides, or major surfaces of the substrate). For example, distortion could include shrinkage in the x-y plane of a substrate and/or expansion in the x-y plane of the substrate.
The term “CTE matched material” and the like as used herein means a material that has a coefficient of thermal expansion (CTE) which differs from the CTE of a reference material by less than about 20 percent (%). Preferably, the CTEs differ by less than about 10%, 5%, 3%, or 1%.
The term “flexible substrate” as used herein means a free-standing substrate that readily adapts its shape. Accordingly, in many embodiments, the flexible substrate can comprise (e.g., consist of) a flexible material, and/or can comprise a thickness (e.g., an average thickness) that is sufficiently thin so that the substrate readily adapts in shape. In these or other embodiments, a flexible material can refer to a material having a low elastic modulus. Further, a low elastic modulus can refer to an elastic modulus of less than approximately five GigaPascals (GPa). In some embodiments, a substrate that is a flexible substrate because it is sufficiently thin so that it readily adapts in shape, may not be a flexible substrate if implemented with a greater thickness, and/or the substrate may have an elastic modulus exceeding five GPa. For example, the elastic modulus could be greater than or equal to approximately five GPa but less than or equal to approximately twenty GPa, fifty GPa, seventy GPa, or eighty GPa. Exemplary materials for a substrate that is a flexible substrate because it is sufficiently thin so that it readily adapts in shape, but that may not be a flexible substrate if implemented with a greater thickness, can comprise certain glasses (e.g., fluorosilicate glass, borosilicate glass, Corning® glass, Willow™ glass, and/or Vitrelle glass, etc., such as, for example, as manufactured by Corning Inc. of Corning, New York, United States of America, etc.) or silicon having a thickness greater than or equal to approximately 25 micrometers and less than or equal to approximately 100 micrometers.
Meanwhile, the term “rigid substrate” as used herein can mean a free-standing substrate that does not readily adapt its shape and/or a substrate that is not a flexible substrate. In some embodiments, the rigid substrate can be devoid of flexible material and/or can comprise a material having an elastic modulus greater than the elastic modulus of a flexible substrate. In various embodiments, the rigid substrate can be implemented with a thickness that is sufficiently thick so that the substrate does not readily adapt its shape. In these or other examples, the increase in rigidity of the carrier substrate provided by increasing the thickness of the carrier substrate can be balanced against the increase in cost and weight provided by increasing the thickness of the carrier substrate.
As used herein, “polish” can mean to lap and polish a surface or to only lap the surface.